Theoretical models specify that anxiety aggregates in families. Research confirmed maternal anxiety as a predictor of childhood anxiety; however, very little evidence exists in support of paternal anxiety's role in child anxiety as well as about potentially reciprocal relationships between parental and child anxiety. The parent-child anxiety transmission mechanisms are also not fully understood; the majority of previous research focuses on the child's acquisition of anxiety symptoms from a parent via cognitive processes. Recent integrative theoretical models propose that child emotion regulation processes might be involved in parent-child anxiety transmission. The current dissertation aimed to address these gaps in literature. Both studies utilized data from over 800 mothers, 400 fathers, and their children drawn from the longitudinal NICHD Study of Early Childcare and Youth Development. Measures of maternal anxiety, paternal anxiety, child anxiety, and child emotion dysregulation were collected over a nine-year period when children were between the ages of 6 and 15 years. Study I provided evidence of significant indirect effects from parental anxiety to child anxiety through child emotion dysregulation for both mother-child and the father-child relationships. Child emotion dysregulation was non-significant in the father-child path of a family model, despite significant direct effects. The results provide evidence for child emotion dysregulation as an underlying process of parent-child anxiety transmission. Study II provided evidence of significant bidirectional predictive links of maternal anxiety and child anxiety across ages 6, 8, 10, and 15 years tested in a mother-child cross-lagged path model. Significant predictive paths from paternal anxiety to child anxiety were found from ages 6 to 8 and a significant predictive path from child anxiety to paternal anxiety was found from age 10 to age 15 in a father-child cross-lagged model. Additional tests of family models confirmed that there were unique effects of both maternal and paternal anxiety on child anxiety over time. The results show the long-term impact of both maternal anxiety and paternal anxiety on child anxiety as well as child anxiety's reciprocal effects on parental anxiety. Both studies demonstrate the importance of both mothers and fathers in childhood anxiety etiology. / Doctor of Philosophy / Research has shown that anxiety might run in families, and that parental and child anxieties might reinforce each other. In research, most attention is paid to mothers and how their anxiety influences child anxiety, including how children learn their anxious experiencing from their mothers. Very little research has been dedicated to studying fathers and how their anxiety might impact their children. The current two studies of this dissertation wanted to better understand how maternal and paternal anxiety shape child anxiety over the years. Study I tested whether the way how children regulate their emotions is influenced by parental anxiety and whether it contributes to their own anxiety. The evidence shows both mother and father anxiety influence children's regulation of their emotions, and in turn, this contributes to child anxiety. Therefore, how children control their emotions impacts how parental anxiety shapes child anxiety. Study II tested whether parental anxiety influences child anxiety consistently over time as children become adolescents. Study II also tested whether child anxiety contributes to parental anxiety over the years. Results showed that maternal and child anxiety consistently foretold each other when children were at 8, 10, and 15 years old. The results for fathers were more complicated and showed that father anxiety likely influences child anxiety when children are younger, while child anxiety influences paternal anxiety when children are older, during their teenage years. Both studies highlighted showed the importance of both mother and father anxiety to better understand child anxiety.